Effect of Rotation Age and Thinning Regime on Visual and Structural Lumber Grades of Douglas-Fir Logs

Douglas-fir, the most important timber species in the Pacific Northwest, US (PNW), has high stiffness and strength. Growing it in plantations on short rotations since the 1980s has led to concerns about the impact of juvenile/mature wood proportion on wood properties. Lumber recovered from four sites in a thinning trial in the PNW was analyzed for relationships between thinning regime and lumber grade yield. Linear mixed-effects models were developed for understanding how rotation age and thinning affect the lumber grade yield. Log small-end diameter was overall the most important for describing the presence of an appearance grade, generally exhibiting an indirect relationship with the lower quality grades. Stand Quadratic Mean Diameter (QMD) was found to be the next most uniformly important predictor, its influence (positive or negative) depending on the lumber grade. For quantity within a grade, as log small-end diameter increased, the quantity of the highest grade increased, while decreasing the quantity of the lower grades differentially. Other tree and stand attributes were of varying importance among grades, including stand density, tree height, and stand slope, but logically depicted the tradeoffs or rebalancing among the grades as the tree and stand characteristics change. Structural lumber grade presence was described best by acoustic wave flight time, log position (decreasing presence in upper logs), and an increasing presence with rotation age. A smaller set of variables proved useful for describing quantity within a structural grade. Forest managers can use these results in planning to best capture value in harvesting, allowing them to direct raw materials (logs) to appropriate manufacturing facilities given market demand.

Epicormic Branches Affect Lumber Grade and Value in Willow Oak

A case study was conducted in a 50-yr-old bottomland oak stand in central Alabama to investigate the relationship between epicormic branches and lumber grade and value in willow oak (Quercus phellos L.). The stand had been thinned from below 7–10 yr earlier, resulting in a wide variety of epicormic branch conditions on the residual trees. A sample of 41 willow oak trees was selected before the stand was clearcut in late 1991. All merchantable logs in each tree were graded prior to felling. Average dbh of sampled trees was 19.1 in. Each tree averaged 9.5 epicormic branches on the sawlog portion of the bole. From these 41 trees, a random sample of 57 logs (31 butt logs and 26 upper logs) was shipped to a sawmill where they were sawn into lumber and graded. Epicormic branching had a large detrimental effect on log grade of individual trees. In general, as few as five epicormic branches somewhat evenly distributed on a 16 ft log was enough to cause a reduction in log grade. More importantly, defects caused by epicormic branches had a serious effect on lumber grade, particularly in the higher grades. Over 50% of the lumber volume that would have been graded as either First and Seconds or Select in the absence of epicormic branches was downgraded to No. 1 Common or below due to defects caused by epicormic branches. Based on lumber prices prevailing at the time of the study, defects caused by epicormic branches resulted in a 13% reduction in the value of the lumber produced in the final harvest. South. J. Appl. For.25(3):136–141.

A performance evaluation of edging and trimming operations in U.S. hardwood sawmills

Edger and trimmer operators must make constant decisions in short time periods on the amount of materials to remove from boards produced in the sawmill. Their decisions directly affect the total volume, grade, and value of the boards, and they therefore directly affect the total value of lumber produced. In recent years, many softwood sawmills have installed computer controlled edgers and trimmers with scanners and optimizers to achieve higher recovery rates. Before similar, relatively expensive, technologies can be seriously evaluated for the hardwood industry, however, the current performance of edging and trimming operations must be known. Using a sample of 3360 boards, compiled from 37 hardwood sawmills located in 16 states, lumber grade, length, width, and dollar values obtained in edging and trimming operations were compared with values predicted by USDA Forest Service scientists for the same lumber. Significant differences between edging and trimming performance and predicted values were determined via statistical tests. A linear regression model was formulated to study the influence of overedging, overtrimming, and grade difference on the percentage of predicted dollar value achieved. It was found that most sawmills edged a relatively low proportion of their total production. In 99% of the boards, edging and trimming operations achieved similar values for grade and length to those predicted by the USDA scientists. The value of the lumber increased significantly as the amount of overedging decreased.

Timber quality classes from cruise data for lodgepole pine sawn at a board mill in British Columbia

Information on timber quality can play an important role in a wide range of planning activities at sawmills. A system for assessing timber quality does not exist for lodgepole pine (Pinuscontorta Dougl.), which is one of the most important commercial species in the interior of British Columbia. A classification system for lodgepole pine timber was developed from cruise data collected according to procedures prescribed by the British Columbia Ministry of Forests. A sawmill lumber yield study was made to obtain the data necessary to test the grading system. Regression analysis, likelihood ratio tests, and analysis of variance were used to test for significant differences in lumber grade yields and log values among six quality classes. The findings indicate that data collected during cruising can be used to separate timber into distinct quality classes. The quality classes showed appreciable variation in average log value when current lumber prices were applied.